The present invention relates to the technical field of electrical capacitors.
A considerable proportion of the faults, and more particularly parasitic resistances which occur in electrolytic filter capacitors occur in the hermetic bushings for the terminals and in the latter. At present these terminals are inserted in the form of approximately cylindrical members made from light alloy or aluminium in a cover made from a thermosetting plastic of an aluminium case shaped by extruding. Such terminals are fixed in the cover material at the time of moulding and in each case comprise:
A THREADED HOLE FOR RECEIVING A CLAMPING SCREW FOR CONNECTING A LUG TO THE LOAD CIRCUIT;
CONNECTING SLEEVES PROVIDED WITH UNEVEN SURFACES WHICH BRING ABOUT A KEYING IN ROTATION AND WHICH ENVELOP THE TIGHTENING TORQUES OF THE SCREW, WHICH IN ADDITION INCREASE THE LENGTH OF THE LEAKAGE PATHS OF THE ELECTROLYTE WITHIN THE CASE;
AN INNER CONNECTING MEMBER ON WHICH IS WELDED, RIVETED OR BOTH WELDED AND RIVETED A CONNECTION TO THE INTERNAL CAPACITATIVE MEMBER.
As an example, a capacitor having a capacitance of 47,000 .mu.F under a continuous operating voltage of 6 V, a cover with a diameter of 72 mm is provided to seal the case having terminals with a diameter of 11 mm, although the surface area which they occupy only represents 4.7% of that of the cover. In such a capacitor the minimum impedance as a function of the frequency is 10 mOhm and the series resistance introduced by the terminals is 1 mOhm.
It can be seen that the cross-section of the terminals is too small to ensure that the heat emitting within the case is correctly removed by these terminals with a good thermal conductivity when the capacitor is subjected to a high alternating current load.
The internal connecting lugs can only be fixed to each terminal via a single member. This is troublesome when the number of the said lugs is increased in order to reduce the series resistance and self-induction of the capacitative members produced in the form of coils.
Finally, when the capacitor is not connected to the load circuit by means of lugs and cables, but is connected on connecting bars called busbars, the mounting provided by two screws is weak relative to the vibrations which occur. If the capacitor is mounted in this manner in the horizontal position it can oscillate and become detached, so it is necessary to fix it by means of a supplementary clip.